1. Field of the Invention
This invention relates to a durable hydrophilic fiber. More specifically, this invention relates to a durable hydrophilic fiber and a fabric obtainable by using the fiber, useful mainly as a surface layer or a second sheet of the hygienic materials such as disposable diaper or sanitary napkin, as a shape preserver for water absorbing products, or further as industrial and medical wiping cloths.
2. Description of the Related Art
Hygienic articles such as a disposable diaper are formed of three layers of a surface material, an absorbing material and a backing material in the order from the side contacting directly to the skin. The surface material is required to possess good water permeability for rapid transmission of liquid to be absorbed to the absorbing material and also good dry touch which prevents absorbed liquid to flow back and provides skin dry feeling. It is preferable to be hydrophilic to improve water permeability. However, on the other hand, it is preferable to be hydrophobic to improve dry touch.
To achieve this paradoxical purpose, a non-woven fabrics made of polyolefin or polyester type fiber to which small amount of surface active agent is applied to afford desired hydrophilicity. (JP-A-63-6166; JP-A-63-49158)
However such surface materials using fiber to which surface active agent is applied have a drawback that, after once or twice liquid absorption, water permeability decreases rapidly caused by efflux of surface active agent resulting in unpleasant feeling due to remaining of liquid on the surface material.
Also known is a non-woven fabric made of durable hydrophilic fiber to which a surface active agent containing a water-soluble modified silicone is applied thus reducing the efflux of applied surface active agent and keeping hydrophilicity after repeated water transmission (JP-A-63-303184; JP-A-1-148879; JP-A-1-148880; JP-A-2-169774; JP-A-3-59169). However, such non-woven fabrics or knit/woven textiles consisting of durable hydrophilic fiber with these surface active agents, though showing comparatively good durable hydrophilicity, due to the water-soluble modified silicone contained as the necessary component, had a problem of poor strength of web or non-woven laminates caused by reduced friction between fibers. Further it was a problem that, in the stage of winding non-woven product, wound-up shape is unstable due to over flatness between non-woven webs.
According to JP-B-3-50030, it is proposed that hydrophilic polyolefin fiber can be achieved by applying the mixture of surface active agents such as alkylene oxide adduct to the compound having alkylolamide and active hydrogen or alkyl phosphate and so on. However this process cannot give enough durable hydrophilicity and anti-electrostaticity.